On the home page click on "User CP" on the center column
This will bring up settings. Scroll down and you will see "edit avatar" under "My Settings". Click on the edit avatar and you can upload an avatar.

Edit your Avatar

To add/edit your avatar click on settings at the top of the page, right hand side. Look in the left hand column under My Settings and the My Profile. You should see the link for edit avatar. Click the link and upload your image.